feat(dialogs): gedeelde primitives — useDirtyCloseGuard, useDialogSubmitShortcut, layout-classes

Story 1 van PBI "Alle dialogen conform docs/patterns/dialog.md".

- components/shared/use-dirty-close-guard.tsx — hook + paired AlertDialog
- components/shared/use-dialog-submit-shortcut.ts — Cmd/Ctrl+Enter handler
- components/shared/entity-dialog-layout.ts — MD3-conforme classes voor §4
- TaskDialog refactored om beide hooks + classes te gebruiken (geen
  gedragsverandering)
- 8 nieuwe unit-tests

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

components/shared/entity-dialog-layout.ts

@@ -0,0 +1,16 @@
+import { cn } from '@/lib/utils'
+
+export const entityDialogContentClasses = cn(
+  'flex flex-col p-0 gap-0',
+  'max-h-[90vh] w-full max-w-[calc(100%-2rem)]',
+  'sm:max-w-[90vw] sm:max-h-[85vh]',
+  'lg:max-w-[50vw] lg:min-w-[480px]',
+)
+
+export const entityDialogHeaderClasses =
+  'flex items-center justify-between px-6 pt-5 pb-4 border-b border-outline-variant shrink-0'
+
+export const entityDialogBodyClasses = 'flex-1 overflow-y-auto px-6 py-6 space-y-6'
+
+export const entityDialogFooterClasses =
+  'border-t border-outline-variant px-6 py-4 shrink-0'